Pouch case for secondary battery and pouch type secondary battery including the same

ABSTRACT

A pouch case of the present disclosure includes an inner resin layer, a metallic layer, and an outer resin layer, wherein the resin layer(s) include(s) a foaming activator containing an isocyanate-based compound and a polyol compound. Accordingly, since the pouch case includes the inner resin layer and/or the outer resin layer including the foaming activator, when moisture or the like is permeated thereto due to an external factor, a protective layer including urethane-based foam is formed in the outer resin layer or between the inner resin layer and an electrode assembly in a short time, so that the pouch case and the electrode assembly may be protected, moisture which is permeable into the electrode assembly may be blocked, and separator cracking also may be prevented. Accordingly, explosion which may be caused by moisture permeation, separator cracking, or a short circuit by contact between the pouch case and the electrode assembly, or the like, may be prevented, and stability of a pouch type secondary battery may thus be ensured.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No.10-2014-0153658 filed on Nov. 6, 2014 in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a pouch case for a secondary batteryand a pouch type secondary battery including the same, and particularlyin a pouch case including an inner resin layer, a metallic layer, and anouter resin layer for enhanced stability, to a pouch case for asecondary battery and a pouch type secondary battery including the same,wherein the inner resin layer and/or the outer resin layer include(s) afoaming activator capable of forming urethane-based foam.

2. Description of the Related Art

Technological developments and increased demands for mobile devices haveled to a rapid increase in demands for secondary batteries as energysources. Accordingly, researches for secondary batteries capable ofmeeting a variety of needs are emerging.

There are high demands for a prismatic type lithium secondary batteryand a pouch type lithium secondary battery in terms of shape, which havea small thickness and are thus applicable to, for example, cell phones;and a lithium cobalt polymer secondary battery in terms of material,which has high energy density, discharge voltage, and stability.

The prismatic type lithium secondary battery is advantageous inprotecting an electrode assembly against external impact and subjectedto an easy injection process, but has a difficulty in reducing volumedue to a fixed shape. Therefore, electric devices which use theprismatic type lithium secondary battery as a power source have ashortcoming in terms of a restricted design. Moreover, in terms ofstability, the prismatic type lithium secondary battery has shortcomingsin that gas or liquid is not smoothly vented and the risk of explosionthus increases due to accumulation of internal heat and gas, andineffective release of internal heat results in cell degradation due tooverheat in a short period of time.

The pouch type lithium secondary battery has advantages in that thepouch type lithium secondary battery is suitable for manufacturing athin cell due to no restriction on its shape and size; it is easy toassemble the pouch type lithium secondary battery through heat fusion;and the pouch type lithium secondary battery has high stability due toeasy vent of gas or liquid under the condition of abnormal behaviors.However, the pouch type secondary battery uses a thin soft laminatedsheet (pouch) as a case thereof unlike the prismatic type, and thus hasshortcomings in terms of low physical and mechanical strength, lowsealing reliability, and low stability against external impact and thelike.

Particularly, when large current flows into the pouch type secondarybattery in a short time by local crush such as high temperatureexposure, overcharge, an external short circuit, impurities inelectrodes, and nail penetration, the electrode coated with an activematerial serves as a heat source and generates heat which thus rapidlyincreases temperature of the battery, so that reactions between anelectrolytic solution and the electrode are accelerated and ignition ofthe battery is thus induced. In addition, an increase in internalpressure of the battery due to a gas generated by the reaction betweenthe electrolytic solution and the electrode results in problems ofswelling and explosion of the secondary battery. Such a risk ofexplosion may be the most critical drawback of lithium secondarybatteries because the risk of explosion leads to a serious problem instability.

Thus, an essential consideration in developing a pouch type secondarybattery is to ensure its stability.

Using a pouch case having a high strength for stability ensuresstability against external impact, but has a shortcoming in that it isdifficult to form such a pouch case. In order to remedy thisshortcoming, a method for improving the strength of a battery by using asoft pouch case and further forming a separate reinforcement layer onthe surface thereof is suggested. However, in such a case, a separatereinforcement layer should be additionally provided, so that the size,volume, and manufacturing costs of the battery disadvantageouslyincrease.

SUMMARY OF THE INVENTION

The present disclosure provides a pouch case for a secondary battery,which prevents the risk such as battery explosion caused by, upon acrack or rupture of a pouch case by an external factor, moisturepermeation, separator cracking, or a short circuit by contact between apouch case and an electrode assembly, and thus ensures stability.

A pouch case according to an embodiment of the present disclosureincludes an inner resin layer, a metallic layer, and an outer resinlayer, wherein at least one resin layer of the inner resin layer and theouter resin layer includes a foaming activator, wherein the foamingactivator includes an isocyanate-based compound and a polyol compound.

The particle diameter of the foaming activator included in the innerresin layer may be 50% or less of the thickness of the inner resinlayer, and the particle diameter of the foaming activator included inthe outer resin layer may be 50% or less of the thickness of the outerresin layer.

The content of the foaming activator included in the inner resin layermay be 30 vol % or less of the total volume of the inner resin layer,and the content of the foaming activator included in the outer resinlayer may be 30 vol % or less of the total volume of the outer resinlayer.

The isocyanate-based compound may include any one selected from thegroup consisting of benzylisocyanate, phenylisocyanate, isoprenediisocyanate (IPDI), methylene diphenyl diisocyanate (MDI), toluenediisocyanate (TDI), and a combination thereof.

The polyol-based compound may be at least any one selected from thegroup consisting of polyester polyol compounds and polyether polyolcompounds.

The polyether polyol-based compound may include polytetramethylene etherglycol (PTMG).

In the pouch case, a protective layer including urethane-based foam maybe formed, on an outer surface of the inner resin layer, by aurethane-based foaming reaction between a foaming activator includingthe isocyanate-based compound and the polyol compound, and any onefoaming agent selected from the group consisting of water, carbondioxide, and nitrogen, which are caused by an external factor, and acombination thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent disclosure will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a perspective view schematically illustrating a structure of aconventional pouch case having conventional layers of inner resinlayer/metallic layer/outer resin layer;

FIG. 2 is a sectional view schematically illustrating a structure of apouch case having layers of inner resin layer/metallic layer/outer resinlayer wherein the inner resin layer includes a foaming activatoraccording to an embodiment of the present disclosure;

FIG. 3 is a sectional view illustrating that a protective layer isformed, due to an external factor, in a pouch case having layers ofinner resin layer/metallic layer/outer resin layer wherein the innerresin layer includes a foaming activator according to an embodiment ofthe present disclosure;

FIG. 4 shows an apparatus for a rupture test of a pouch type secondarybattery under an external factor;

FIG. 5 shows a pouch type secondary battery in which a protective layeris formed by foaming according to an embodiment of the presentdisclosure;

FIG. 6 shows a conventional pouch type secondary battery without aprotective layer; and

FIG. 7 is a graph showing results of rupture tests of pouch typesecondary batteries.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments of the present disclosure will now be described indetail with reference to the accompanying drawings. Terms or words usedin this specification and claims should not be restrictively interpretedas ordinary or dictionary-based meanings, but should be interpreted asmeanings and concepts conforming to the inventive concept on the basisof the principle that an inventor can properly define the concept ofterms to explain his or her own invention in the best ways.

As illustrated in FIG. 1, a conventional pouch type case includes aninner resin layer 11 acting as a sealer, a metallic layer 17 which actsas a barrier layer against moisture and oxygen while maintainingmechanical strength, and an outer resin layer 19 acting as a substrateprotecting layer, and an electrode assembly is disposed on one surfaceof the inner resin layer with the opposite surface being in contact withthe metallic layer.

In general, the inner resin layer includes casted polypropylene (CPP),the metallic layer includes an aluminum layer, and the outer resin layerincludes a multi-layered structure in which a polyethylene terephthalate(PET) layer and a nylon layer are stacked.

In this case, the casted polypropylene layer as the inner resin layerhas disadvantages in that cracks may be generated during a heat fusionprocess for sealing or the layer is easily ruptured by impact, which isa cause of moisture permeation into a pouch type secondary battery andthus leads to battery explosion and the like. Consequently, this leadsto stability degradation of the pouch type secondary battery.

To solve the above-described problems, a pouch case for a secondarybattery, according to an embodiment of the present disclosure, includesan inner resin layer, a metallic layer, and an outer resin layer,wherein the inner resin layer and/or the outer resin layer include (s) afoaming activator containing an isocyanate-based compound and a polyolcompound.

Furthermore, a pouch type secondary battery according to anotherembodiment of the present disclosure includes an electrode assemblyincluding a positive electrode, a negative electrode, a separator, andan electrolyte; and the pouch case receiving the electrode assembly.

Hereinafter, the present disclosure will be described in more detailwith reference to the accompanying drawings.

First, a pouch case for a secondary battery, according to an embodimentof the present disclosure, may include a foaming activator in an innerresin layer and/or an outer resin layer.

FIG. 2 illustrates an electrode assembly 25 and a pouch case having aninner resin layer 21 and an outer resin layer 29 which cover a surfaceof the electrode assembly 25 wherein the inner resin layer 21 includesfoaming activators 23, in which only one surface is illustrated, but thepouch case may cover both surfaces of the electrode assembly.

As illustrated in FIG. 2, the pouch case of the present disclosure maybe configured in such a way that the inner resin layer 21 is disposedinside the pouch, where the inner resin layer 21 is in contact with theelectrode assembly 25, particulates of foaming activator 23 arehomogeneously dispersed in the inner resin layer 21, and a metalliclayer 27 is stacked on one surface of the inner resin layer 21 with theopposite surface being in contact with the electrode assembly 25.Furthermore, an outer resin layer 29 which is the outermost member ofthe pouch case may be stacked on one surface of the metallic layer 27with the opposite surface being in contact with the inner resin layer21, and particulates of foaming activator 23 may be homogeneouslydispersed even in the outer resin layer 29.

Examples of the foaming activator may include, without limitation, anycompound which reacts with a foaming agent such as water, carbondioxide, or nitrogen to induce a resin reaction and generateurethane-based foam. For example, an isocyanate-based compound and apolyol-based compound may be used as the foaming activator.

The isocyanate-based compound may be generally expressed as R—N═N═O,where R may be hydrocarbon, and the hydrocarbon may be straight-chain orbranched, linear or cyclic, saturated or unsaturated, and aliphatic oraromatic. Furthermore, although the hydrocarbon may include a functionalgroup such as an alcohol group, an ether group, an ester group, and acarbonyl group, it may be preferable that the hydrocarbon does notinclude the functional group in term of reactivity with a resin whichmay be a material of the inner resin layer, reactivity with the foamingagent, and reactivity with a generated gas.

Specifically, for example, the isocyanate-based compound may bebenzylisocyanate, phenylisocyanate, isoprene diisocyanate (IPDI),methylene diphenyl diisocyanate (MDI), toluene diisocyanate (TDI), or acombination thereof, but these examples do not exclude applicability ofother isocyanate compounds.

The polyol-based compound may be at least any one selected from thegroup consisting of polyester polyol compounds and polyether polyolcompounds.

The polyether polyol-based compound may be, for example,polytetramethylene ether glycol (PTMG) or the like.

The isocyanate-based compound and the polyol-based compound may be usedas being properly mixed considering equivalence ratio used in a urethanereaction. Although the mixing ratio is not particularly limited, unlesseither of the compounds is used in excess, for example, 80% or more, aprotective layer including urethane-based foam may be formed by properlycontrolling a gas evolution reaction between the foaming agent and theisocyanate-based compound and a urethane formation reaction between theisocyanate-based compound and the polyol compound.

The urethane-based foam may include a urethane-based polymer such aspolyurethane, and may be formed by means of gas bubbles generated in acompound such as polyurethane by the gas evolution reaction which takesplace together with the urethane reaction. This urethane-based foam mayinclude polyether-based foam and polyester-based foam, thepolyester-based foam is rigid foam having excellent heat resistance andsolvent resistance and may prevent short circuit caused by externalimpact, and the polyether-based foam has excellent elasticity, so thatproperly mixed foam may be preferable in terms of short circuitprevention from impact by external factors or battery operation.

FIG. 3 illustrates that a protective layer 34 including urethane-basedfoam is formed between an electrode assembly 35 and an inner resin layer31 when impact is applied to a battery due to an external factor 38 anda crack is thus generated in a pouch case.

As illustrated in FIG. 3, the foaming agent such as water, carbondioxide, or nitrogen, which reacts with a foaming activator 33, may beintroduced due to the external factor 38. In this case, by a urethanereaction, a gas evolution reaction of the isocyanate compound, and thelike, the foaming activator 33 may react with the foaming agent to formurethane foam. Accordingly, a metallic layer 37 and an outer resin layer39 as well as the inner resin layer 31 may be bent like a bow due tovolume expansion caused by internal gas generation, and the generatedgas may thus form a protective layer 34 between the inner resin layer 31and the electrode assembly 35.

In the case where the foaming agent is introduced due to the externalfactor 38, the external factor 38 means a needlelike object, a bluntobject, or the like, and the introduction of the foaming agent may meanthe case where a crack or hole is generated in the pouch case understrong impact by such an object such that the internal electrodeassembly may be damaged.

Thus, the protective layer 34 may be formed in a space between the innerresin layer 31 and the electrode assembly 35 in contact with the innerresin layer 31, and urethane-based foam may be partially formed even inthe outer resin layer because the foaming activator 33 is also includedin the outer resin layer 39.

Due to the protective layer 34 including the urethane-based foam, theinner resin layer 31, the metallic layer 37, and the outer resin layer39 may be formed in such an arcuate shape that the central portionsthereof are more expanded than both ends thereof. Such a protectivelayer 34 may act as a sealer like the inner resin layer 31, and theformation of the protective layer 34 prevents moisture permeation intothe electrode assembly 35, separator cracking, or the like which iscaused by the external factor, and may thus prevent the risk such asexplosion caused by a short circuit or the like by contact between thepouch case and the electrode assembly 35.

The foaming activator may be, but is not limited to, in the form ofnearly spherical particles. When the foaming activator is in the form ofnearly spherical particles, the particle diameter thereof may be about60 μm or less.

In selecting the particle size of the foaming activator with respect tothe thickness of the two resin layers, it may be preferable that theparticle size is not greater than about 50% of the thickness of theinner resin layer and/or the outer resin layer, and it may be necessaryto properly control the particle size according to the thickness of thetwo resin layers.

When the particle diameter of the foaming activator is greater thanabout 50% of the two resin layers, the particle size is excessivecompared with the thickness of the resin layers, so that there ispossibility to interfere with the sealing role of the inner resin layerin the absence of external impact, and when the foaming activator isexcessively formed in the outer resin layer, there is possibility toreduce bending properties because urethane foam is rigid.

Furthermore, it is preferable that the foaming activator ishomogeneously dispersed in the inner resin layer and/or the outer resinlayer. Since the foaming activator may react with a small amount ofmoisture, there is no critical problem even if the foaming activator isnot homogeneously dispersed. However, in order to serve to preventmoisture permeation by forming a protective layer in a short time, itmay be preferable that the foaming activator is homogeneously dispersedthroughout the resin layer.

Also, the content of the foaming activator may be about 30 vol % or lessof the total volume of each of the inner resin layer and/or the outerresin layer. As in the particle size, it is necessary to properlycontrol the amount of the foaming activator with respect to the volumeof the inner resin layer.

The inner resin layer may have a thickness of 40 to 120 μm. The innerresin layer may be made of, for example, any one selected from the groupconsisting of polypropylene, casted polypropylene, apolypropylene-butylene-ethylene ternary copolymer, polypropylenechloride, polyethylene, an ethylene-propylene copolymer, apolyethylene-acrylate copolymer, a polypropylene-acrylate copolymer, anda combination thereof.

The metallic layer may have a thickness of 20 to 100 μm. The metalliclayer may be made of, for example, an alloy of iron (Fe), carbon (C),chromium (Cr), and manganese (Mn), an alloy of iron (Fe), carbon (C),chromium (Cr), and nickel (Ni), or aluminum (Al). It may be preferablethat aluminum is used as the metallic layer.

The outer resin layer may have a thickness of 10 to 100 μm. The outerresin layer may include, for example, a single layer of one, or amulti-layer of two or more, selected from the group consisting ofpolyethylene, polypropylene, polyethylene terephthalate, nylon, lowdensity polyethylene (LDPE), high density polyethylene (HDPE), andlinear low density polyethylene (LLDPE).

As described above, the pouch case of the present disclosure includesthe isocyanate-based compound and the polyol-based compound in the innerresin layer thereof. Therefore, when the foaming agent such as watercaused by an external factor is introduced, the protective layerincluding urethane-based foam is formed between the inner resin layerand the electrode assembly in a short time, so that the pouch case andthe electrode assembly may be protected, moisture which is permeableinto the electrode assembly may be blocked, and separator cracking alsomay be prevented.

Accordingly, explosion which may be caused by moisture permeation,separator cracking, or a short circuit by contact between the pouch caseand the electrode assembly, or the like, may be prevented, and stabilityof a pouch type secondary battery may thus be ensured.

Furthermore, the present disclosure provides a pouch type secondarybattery including an electrode assembly, and the pouch case of thepresent disclosure, which receives the electrode assembly.

In this case, the assembly is configured in such a way that a negativeelectrode including a negative electrode active material and a positiveelectrode including a positive electrode active material are insulatedwith each other and coiled, with a separator disposed therebetween.

Specifically, the positive electrode is prepared in such a way that apositive electrode collector is coated with a mixture of the positiveelectrode active material, a conducting agent, and a binder, and thendried. A filler may be added to the mixture if necessary.

The positive electrode active material according to the presentdisclosure may be used as being mixed with a compound mainly including alithium intercalation material such as a layered compound such as alithiated cobalt oxide (LiCoO₂) or a lithiated nickel oxide (LiNiO₂),which is substituted with one or more transition metals; a lithiatedmanganese oxide (LiMnO₂) of which chemical formula is expressed byLi_(1+x)Mn_(2−x)O₄ (where, 0≦x≦0.33), LiMnO₃, LiMn₂O₃, or LiMnO₂; alithiated copper oxide (Li₂CuO₂); a vanadium oxide such as LiV₃O₈,LiFe₃O₄, V₂O₅, or Cu₂V₂O₇; a lithiated nickel oxide of which chemicalformula is expressed by LiNi_(1−x)M_(x)O₂ (where, M is Co, Mn, Al, Cu,Fe, Mg, B, or Ga, and 0.01≦x≦0.3); a lithiated manganese composite oxideof which chemical formula is expressed by LiMn_(2−x)M_(x)O₂ (where, M isCo, Ni, Fe, Cr, Zn, or Ta, and 0.01≦x≦0.1) or Li₂Mn₃MO₈ (where, M is Fe,Co, Ni, Cu, or Zn); a LiMn₂O₄ in which lithium is partially substitutedwith alkaline earth metal ions; a disulfide compound; Fe₂(MoO₄)₃ or acomposite oxide formed by a combination thereof.

The positive electrode collector is generally prepared to have athickness of 3 to 500 μm. The positive electrode collector is notparticularly limited as long as it has a high conductivity withoutcausing any chemical change in the battery. For example, stainlesssteel, aluminum, nickel, titanium, baked carbon, or aluminum orstainless steel which is surface-treated with carbon, nickel, titanium,silver, or the like may be used as the positive electrode collector. Thecollector may form fine irregularities on the surface thereof, which mayenhance adhesion to the positive electrode active material, and may bein a variety of forms such as films, sheets, foils, nets, porous bodies,foams, and non-woven fabrics.

The conducting agent is generally added up to 1 to 50 wt % based on thetotal weight of the mixture including the positive electrode activematerial. The conducting agent is not particularly limited as long as ithas conductivity without causing any chemical change in the battery. Forexample, graphite such as natural graphite or artificial graphite;carbon black such as carbon black, acetylene black, ketjenblack, channelblack, furnace black, lamp black, or thermo-black; conductive fiberssuch as carbon fibers or metal fibers; metal powder such asfluorocarbon, aluminum, and nickel powder; conductive whisker such aszinc oxide or potassium titanate; conductive metal oxide such astitanium oxide; conductive materials such as polyphenylene derivativesmay be used as the conducting agent.

The binder is a component for assisting in binding between the activematerial and the conducting agent etc. and in binding to the collector,and is generally added up to 1 to 50 wt % based on the total weight ofthe mixture including the positive electrode active material. Examplesof the binder may include polyvinylidenefluoride, polyvinylalcohol,carboxymethylcellulose (CMC), starch, hydroxypropylcellulose,regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene,polyethylene, polypropylene, ethylene-propylene-diene terpolymers(EPDM), sulfonated EPDM, styrene-butylene rubbers, fluororubbers, and avariety of copolymers.

The filler is an optional component for preventing swelling of thepositive electrode, and is not particularly limited as long as it is afibrous material which does not cause any chemical change in thebattery. For example, olefin polymers such as polyethylene orpolypropylene, and fibrous materials such as glass fibers or carbonfibers are used as the filler.

Furthermore, the negative electrode is prepared in such a way that anegative electrode collector is coated with a negative electrodematerial and then dried. If necessary, the aforesaid components may befurther included therein.

The negative electrode collector is generally prepared to have athickness of 3 to 500 μm. The negative electrode collector is notparticularly limited as long as it has conductivity without causing anychemical change in the battery. For example, copper, stainless steel,aluminum, nickel, titanium, baked carbon, copper or stainless steelwhich is surface-treated with carbon, nickel, titanium, silver, or thelike, or aluminum-cadmium alloys may be used as the negative electrodecollector. Also, as in the positive electrode collector, the negativeelectrode collector may form fine irregularities on the surface thereof,which may enhance adhesion to the negative electrode active material,and may be used in a variety of forms such as films, sheets, foils,nets, porous bodies, foams, and non-woven fabrics.

The negative material includes amorphous carbon or crystalline carbon,and specifically, carbon such as hard carbon or graphite carbon; ametallic composite oxide such as Li_(x)Fe₂O₃ (0≦x≦1), Li_(x)WO₂ (0≦x≦1),or Sn_(x)Me_(1−x)Me′_(y)O_(z) (Me is Mn, Fe, Pb, or Ge; Me′ is Al, B, P,Si, Group I, Group II, or Group III element in the periodic table, orhalogen; 0≦x≦1; 1≦y≦3; and 1≦z≦8; a lithium metal; a lithium alloy; asilicon alloy; a tin alloy; an oxide such as SnO, SnO₂, PbO, PbO₂,Pb₂O₃, Pb₃O₄, Sb₂O₃, Sb₂O₄, Sb₂O₅, GeO, GeO₂, Bi₂O₃, Bi₂O₄, or Bi₂O₅; aconductive polymer such as polyacetylene; or a Li—Co—Ni based materialmay be used as the negative material.

The separator which is disposed between the positive electrode and thenegative electrode and insulates the electrodes, may be, but is notlimited to, a generally known polyolefin-based separator, a compositeseparator in which an organic-inorganic composite layer is formed on anolefin-based substrate, or the like.

The electrode collector having the aforesaid structure is stored in thepouch case, and then an electrolytic solution is injected thereto toprepare a battery.

The electrolytic solution according to the present disclosure is anon-aqueous electrolyte containing a lithium salt, which consists of anon-aqueous electrolyte and lithium. Examples of the non-aqueouselectrolyte include non-aqueous electrolytic solutions, organic solidelectrolytes, and inorganic solid electrolytes.

Examples of the non-aqueous electrolytic solution may include aproticsolvents such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylenecarbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate,γ-butyrolactone, 1,2-dimethoxy ethane, tetrahydroxyfuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolan, formamide,dimethylformamide, dioxolan, acetonitrile, nitromethane, methyl formate,methyl acetate, phosphate triester, trimethoxy methane, dioxolanederivatives, sulfolane, methyl sulfolane,1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives,tetrahydrofuran derivatives, ether, methyl propionate, and ethylpropionate.

Examples of the organic solid electrolyte may include polyethylenederivatives, polyethylene oxide derivatives, polypropylene oxidederivatives, phosphate ester polymers, poly agitation lysine, polyestersulfides, polyvinyl alcohol, polyvinylidene difluorides, and polymersincluding ionic dissociable groups.

Examples of the inorganic solid electrolyte may include lithiumnitrides, lithium halides, and lithium sulfates, such as Li₃N, LiI,Li₅NI₂, Li₃N—LiI—LiOH, LiSiO₄, LiSiO₄—LiI—LiOH, Li₂SiS₃, Li₄SiO₄,Li₄SiO₄—LiI—LiOH, and Li₃PO₄—Li₂S—SiS₂.

The lithium salt is a material which is readily soluble in thenon-aqueous electrolyte. For example, LiCl, LiBr, LiI, LiClO₄, LiBF₄,LiB₁₀Cl₁₀, LiPF₆, LiCF₃SO₃, LiCF₃CO₂, LiAsF₆, LiSbF₆, LiAlCl₄, CH₃SO₃Li,CF₃SO₃Li, (CF₃SO₂)₂NLi, chloroborane lithium, low-molecular weightaliphatic lithium carboxylate, 4-phenyl lithium borate, or imide may beused as the lithium salt.

Furthermore, in order to improve charge/discharge characteristics, fireretardant properties, and the like, for example, pyridine,triethylphosphite, triethanolamine, cyclic ether, ethylene diamine,n-glyme, hexaphosphate triamide, a nitrobenzene derivative, sulfur,quinoneimine dye, N-substituted oxazolidinone, N,N-substitutedimidazolidine, ethylene glycol dialkyl ether, an ammonium salt, pyrrole,2-methoxy ethanol, or aluminum trichloride may be added to thenon-aqueous electrolyte. As applicable, a halogen-containing solventsuch as carbon tetrachloride and trifluoro ethylene may be furtherincluded to impart nonflammability, and carbon dioxide gas may befurther included to improve high temperature storage characteristics.

Meanwhile, the aforesaid pouch type secondary battery is preferably, butnot limited to, a lithium secondary battery.

EXAMPLE

Hereinafter, preferred embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings so thatthose skilled in the art may easily carry out the present disclosure.The present disclosure may, however, be embodied in many different formsand should not be construed as limited to the embodiments set forthherein.

Example 1 1) Preparation Of Electrode Assembly

According to a conventional method used in the art, ternary lithiumcomposite metal oxide (LiMn_(1/3)CO_(1/3)Ni_(1/3)O₂) was used as apositive electrode active material, and the active material was appliedonto an aluminum collector to prepare a positive electrode. Artificialgraphite was used as a negative electrode active material, and theactive material was applied onto a copper collector to prepare anegative electrode. Thereafter, a polyolefin-based separator wasdisposed between the negative electrode and the positive electrode, andthen a non-aqueous electrolytic solution was injected thereto to preparean electrode assembly.

2) Preparation Of Pouch Type Secondary Battery

A polypropylene resin was used as an inner resin layer, a nylon resinwas used as an outer resin layer, and aluminum was used as a metalliclayer. Benzylisocyanate and polyester polyol in the form of capsules(about 50 μm) were added as a foaming activator in the inner resin layerand the outer resin layer, and the inner resin layer, the metalliclayer, and the outer resin layer were stacked in that order to prepare apouch case. In this case, the volume of the foaming activator capsulesincluded in each of the inner resin layer and the outer resin layer wasabout 25 vol % based on the total volume of the each resin layer.

The electrode assembly was placed in the prepared pouch case, and thenthe pouch case was sealed through heat fusion. In order to confirm thata protective layer of polyester-based urethane foam was formed byfoaming with the foaming activator, before the sealing, a cross sectionin a state that the protective layer was formed and the electrodeassembly and the pouch case were stacked was photographed and shown inFIG. 5.

Comparative Example 1

A pouch type secondary battery was prepared using the same materials andthe same method as in Example 1 except that the foaming activator forforming the protective layer was not added to the inner resin layer andthe outer resin layer of the pouch case. Also in this case, before thesealing, a cross section in a state that the electrode assembly and thepouch case were stacked was photographed and shown in FIG. 6.

Experimental Example Rupture Test of Pouch Type Secondary Battery

In order to compare rupture point and magnitude of force that must beapplied for rupture with respect to pouch type secondary batteries ofthe Example 1 and Comparative Example 1, rupture tests were performedusing the pin of UTM apparatus in FIG. 4, and the results were shown inTable 1 and FIG. 7.

TABLE 1 Maximum Rupture at compressive load compressive load Puncture(kgf) (N) (N/μm) Example 1 6.1297 60.1121 0.0601 Comparative 1.586315.5563 0.0156 Example 1

Referring to Table 1 and FIG. 7, it could be seen that in the case ofthe pouch type secondary battery in Comparative Example 1, in which theprotective layer was not formed, the internal electrode assembly wasruptured when force of about 1.59 kgf was applied thereto, and maximumexternal impact against rupture was about 15 N, but in the case of thepouch type secondary battery in Example 1, in which the protective layerwas formed, the internal electrode assembly was not ruptured until forceof about 6.13 kgf was applied thereto, and maximum external impactagainst rupture was about 60 N.

That is, the secondary battery in Example 1 was different in force byexternal impact, against which the internal electrode assembly could beprotected, by about four times from the secondary battery in ComparativeExample 1, and it could be seen that the pouch type secondary battery inExample 1 can protect the internal electrode assembly against evenquadruple impact compared with the pouch type secondary battery inComparative Example 1.

The pouch case of the present disclosure includes the isocyanate-basedcompound and the polyol-based compound in the inner resin layer thereof.Therefore, when the foaming agent such as water caused by an externalfactor is introduced, the protective layer including urethane-based foamis formed between the inner resin layer and the electrode assembly in ashort time, so that the pouch case and the electrode assembly may beprotected, moisture which is permeable into the electrode assembly maybe blocked, and separator cracking also may be prevented.

Accordingly, explosion which may be caused by moisture permeation,separator cracking, or a short circuit by contact between the pouch caseand the electrode assembly, or the like, may be prevented, and stabilityof a pouch type secondary battery may thus be ensured.

While the present disclosure has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

What is claimed is:
 1. A pouch case for a secondary battery, comprisingan inner resin layer, a metallic layer, and an outer resin layer,wherein at least one resin layer of the inner resin layer and the outerresin layer comprises a foaming activator containing an isocyanate-basedcompound and a polyol compound.
 2. The pouch case of claim 1, whereinthe particle diameter of the foaming activator included in the innerresin layer is 50% or less of the thickness of the inner resin layer,and the particle diameter of the foaming activator included in the outerresin layer is 50% or less of the thickness of the outer resin layer. 3.The pouch case of claim 1, wherein the content of the foaming activatorincluded in the inner resin layer is 30 vol % or less of the totalvolume of the inner resin layer, and the content of the foamingactivator included in the outer resin layer is 30 vol % or less of thetotal volume of the outer resin layer.
 4. The pouch case of claim 1,wherein the isocyanate-based foaming activator comprises any oneselected from the group consisting of benzylisocyanate,phenylisocyanate, isoprene diisocyanate (IPDI), methylene diphenyldiisocyanate (MDI), toluene diisocyanate (TDI), and a combinationthereof.
 5. The pouch case of claim 1, wherein the polyol-based foamingactivator is at least any one selected from the group consisting ofpolyester polyol compounds and polyether polyol compounds.
 6. The pouchcase of claim 5, wherein the polyether polyol-based compound comprisespolytetramethylene ether glycol (PTMG).
 7. The pouch case of claim 1,wherein a protective layer comprising urethane-based foam is formed, onan outer surface of the inner resin layer, by a urethane-based foamingreaction among the isocyanate-based foaming activator, the polyol-basedfoaming activator, and any one foaming agent selected from the groupconsisting of water, carbon dioxide, and nitrogen, which are caused byan external factor, and a combination thereof.
 8. The pouch case ofclaim 1, wherein the inner resin layer is made of any one selected fromthe group consisting of casted polypropylene, apolypropylene-butylene-ethylene ternary copolymer, polypropylenechloride, polyethylene, an ethylene-propylene copolymer, apolyethylene-acrylate copolymer, a polypropylene-acrylate copolymer, anda combination thereof.
 9. The pouch case of claim 1, wherein the innerresin layer has a thickness of 40 to 120 μm.
 10. The pouch case of claim1, wherein the metallic layer is made of any one selected from the groupconsisting of aluminum (Al); an alloy of iron (Fe), carbon (C), chromium(Cr), and manganese (Mn); and an alloy of iron (Fe), carbon (C),chromium (Cr), and nickel (Ni).
 11. The pouch case of claim 1, whereinthe metallic layer has a thickness of 20 to 100 μm.
 12. The pouch caseof claim 1, wherein the outer resin layer comprises a single layer ofone, or a multi-layer of two or more, selected from the group consistingof polyethylene, polypropylene, polyethylene terephthalate, nylon, lowdensity polyethylene (LDPE), high density polyethylene (HDPE), andlinear low density polyethylene (LLDPE).
 13. The pouch case of claim 1,wherein the outer resin layer has a thickness of 10 to 100 μm.
 14. Apouch type secondary battery, comprising: an electrode assemblycomprising a positive electrode, a negative electrode, a separator, andan electrolyte; and the pouch case of claim 1 receiving the electrodeassembly.
 15. A battery module comprising the pouch type secondarybattery of claim 14 as a unit cell.
 16. A middle or large devicecomprising the battery module of claim 15 as a power source.